Feeding 1 distribution panel from 2 OCP devices
- Thread starter deerhead
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qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
- Occupation
- Sorta retired........
deerhead said:
Take a look at 240.8
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
I agree. This would be a violation of 240.8.
brian john
Senior Member
- Location
- Leesburg, VA
1. Why?
2. Is this redundant feeds from different sources and one CB is always open.?
2. Is this redundant feeds from different sources and one CB is always open.?
Cold Fusion
Senior Member
- Location
- way north
No where in the NEC that I know of. It deals very little with "practical" or "possible".deerhead said:
I'd be more curious as to why the customer wants to do this.
As brian said, there are reasons why one might want to do this.
cf
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
Problems that could occur are that there is no way to regulate the amount of current that would attempt to flow in each of the feeds. Also, if one breaker tripped, or was turned off, and the panel was loaded above 600A, then the other breaker would become overloaded and trip. Then there is a safety issue, if one was turned off, the panel would still be energized. Finally, if the two breakers were from different sources, then you could have circulating currents flowing causing additional heating. You could also get into a situation with selective coordination under fault conditions.
Besides not meeting 240.8, that should give you a little insight.
Charlie, is your avatar too mean your an old goat?
Besides not meeting 240.8, that should give you a little insight.
Charlie, is your avatar too mean your an old goat?
Cold Fusion
Senior Member
- Location
- way north
So, q, charlie, king, explain why this is different from a double ended sub with a full capacity tie, run with the tie closed. Are there design concerns? Sure. Do they have to be addressed? Yes.
Deer -
I'm not suggesting the advice from q, charlie, and king is wrong. It's just that I couldn't give that advice based on a one line explaination of the installation:
Also, no one has addressed brian's comment - with the information available, it is perfectly valid.
cf
Deer -
I'm not suggesting the advice from q, charlie, and king is wrong. It's just that I couldn't give that advice based on a one line explaination of the installation:
That's not much information to give you a batch of absolutes. I would have to make too many assumptions to arrive at their conclusions.
Also, no one has addressed brian's comment - with the information available, it is perfectly valid.
cf
- Location
- Illinois
- Occupation
- retired electrician
I don't think it is valid with the information that has been provided. It appears to me that they are atempting to serve a 1200 amp load with two 600 amp breakers connected in parallel.
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
- Occupation
- Sorta retired........
don_resqcapt19 said:
That is how I understood it also.
If it is as Brian asked then it sounds like it could be a 1200 amp switch
board fed by a utility to utility transfer switch that will only allow one breaker at a time to feed the switch board. Which would be acceptable.
brian john
Senior Member
- Location
- Leesburg, VA
I agree with Don.
Additionally I see no advantage to doing a set up as described (outside any code issues)
My only point was there are systems with bypasses or dual source feeds operated with one CB open. Generally in these systems the distribution board would be sized the same as one of the input CBs.
Additionally I see no advantage to doing a set up as described (outside any code issues)
My only point was there are systems with bypasses or dual source feeds operated with one CB open. Generally in these systems the distribution board would be sized the same as one of the input CBs.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
The difference is that a double ended LV switchgear line-up is designed to be capable of operating in this capacity, and it would have proper system coordination such that breaker interlocks would trip and block close during a fault on one side or the other to isolate. The bus and mains would also be rated to carry the full capacity. You could also probably guarantee that only qualified personnel would be working on it.Cold Fusion said:
What is being described in the OP does not sound like it fits into this category. Especially since each breaker is 1/2 the rating of the bus. I suppose you would have to shunt trip the second breaker to clear a fault, but I think overall it would be a hard sell to a AHJ. Whereas a double ended switchgear line-up is pretty common and accepted.
- Location
- Massachusetts
brian john said:
It sounds like he is planing on two 600 amp OCPs in parallel to provide 1200 amps which would work (more or less) other then that pesky NEC.:grin:
Cold Fusion
Senior Member
- Location
- way north
kingpb said:
Last edited:
- Location
- Massachusetts
The simplest explanation is usually correct. :smile:
weressl
Esteemed Member
deerhead said:
One way to do it safely is to have the two breakers mechanically tied together so if one trips, the other does too. I would also oversize the conductors by 125% the worse condition tripping range of CB's so if the current difference between the two parallel conductors exceeds the 125% it would trip yet not heated up. Of course if this type overload is to happen then the circuit is useless to begin with.
Another case of Code exception - although it's questionable of you would find an AHJ who would approve it - and technically questionbable installation, but why to do it in the first place?
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